It is rather common to see cargo delivery vehicles equipped with apparatus to aid the driver in placing heavy loads either into or removing it from the truck. One such apparatus is called a "lift gate" which is mounted at the rear end of the truck,s cargo compartment and can be lowered to ground level. The driver moves the load onto the horizontal surface of the lift gate and then operates the gate so as to bring the load up to the level of the bed of the truck. Although such an apparatus is an aid to the driver in that he does not have to lift the heavy load from ground level up to the bed of the truck, or from the truck to the ground, a serious disadvantage is that the driver must still move the load onto the lift gate and then properly position the load within the truck. Another type of apparatus is a swing style crank mounted on a post located usually in the center of the truck bed. Such a crank or crane is commonly used with trucks that carry construction materials. Disadvantages of such an apparatus is that the post eliminates storage space and of course obstructs the positioning of materials on the truck bed. Many of such installations require that the truck not have side walls in the cargo compartment to allow the crane to swing around the perimeter of the truck bed. This of course leaves materials that are to be transported exposed to weather, theft and the like.
Another type of cargo transfer device is a hoist which rides upon rails affixed to the side walls of a trailer. A pair of extension swing booms are pivotally fixed to the rearward end of the rear cargo compartment in such a manner that they can be swung to extend the rail lengths to the exterior of the truck. The extended rail lengths then allow the hoist to move to the exterior of the rearward portion of the rear cargo compartment. Certainly a disadvantage with this type of device relates to the swing boom and the fixation at the rear of the truck. The swing booms, when not in operation, need to be folded across the rear of the truck and, if the rear of the cargo compartment has doors, be folded to a position within the cargo compartment. This eliminates potential cargo space.
Other types of cargo transporting devices have been proposed, but virtually all of them do not have the ability to position a load at virtually any point within the cargo carrying compartment, nor the ability to pick up the cargo from within the compartment at virtually any point and place it on the ground outside of the trailer.